Machines of the above-indicated type are required in particular for arrangement between production machines or primary packaging machines which discharge their products individually and at time intervals which are not absolutely uniform, and packaging machines which introduce those individual products in a group-wise manner into an external packaging such as a cardboard or box, in relatively large numbers. That group-wise packaging operation must take place in a strictly controlled manner in respect of time in order not to involve unnecessary complications in the design and control of the secondary packaging machine.
In addition however grouping and buffer apparatuses of that kind may also be used in connection with other processing lines, for example conversely if products which are supplied in groups in a strictly cyclically controlled manner have to be separated and then passed along at irregular intervals of time. That is the case for example in the electronics industry in regard to supplying automatic fitting machines for electronic circuit boards with the individual electronic components and devices required.
The frequency of failure and stoppage and thus the efficiency of the overall production and packaging line are crucially determined by the operation of bringing the previously individual and separate piece products together to form groups and the step of compensating for irregularities in respect of time in terms of the supply of the individual products. In addition then the speed both at the delivery side and also at the discharge side is often higher relative to the speed of the previous machine so that the speed of the previous machine also determines the production of the overall installation.
German patent specification No 503 342 discloses an arrangement in which a chain carrying entrainment members passes around two horizontally disposed direction-changing or guide wheels. As however the guide wheels are arranged stationarily, there is no possibility of stopping the one run thereof, for example on the receiving side, and at the same time moving the other run which corresponds to the discharge side.
German patent specification No 37 24 839 discloses a similar machine in which the two guide wheels are mounted in a longitudinally displaceable carriage, with the carriage being displaced by way of screws which act thereon at both sides thereof in such a way that as required one of the two runs of the endless conveyor remains at rest while the other run is still moving so that the continuously arriving piece products can be individually received thereby.
That structure operates generally satisfactorily in a practical context but it suffers from the disadvantages in principle that is occupies a relatively large amount of floor area and that the receiving region and the removal region are in different runs of the endless conveyor and therefore the products carried in the endless conveyor must be passed around one of the guide wheels. As a result, when the endless conveyor is operating at high speeds, the products tend to be urged outwardly by the centrifugal force involved. Although it is possible to prevent the products from coming off the endless conveyor by a guide plate or the like, that can nonetheless give rise to problems due to damage to the packs or a restriction in terms of the maximum speed that can be employed.
Furthermore the production of that apparatus is complex and expensive, both from the mechanical point of view and also in terms of the controls involved.